Field of the Disclosure
Embodiments of the present disclosure relate to a thin film transistor substrate including an oxide semiconductor layer, and a display device.
Discussion of the Related Art
A transistor is widely used as a switching device or a driving device in electric fields. Especially, a thin film transistor may be easily manufactured on a glass substrate or a plastic substrate, whereby the thin film transistor may be used as a switching device in a display device such as a liquid crystal display device or an organic light emitting device.
According to a material for an active layer, the thin film transistor may be largely classified into an amorphous silicon thin film transistor using an amorphous silicon active layer, a polycrystalline silicon thin film transistor using a polycrystalline silicon active layer, and an oxide semiconductor thin film transistor using an oxide semiconductor active layer.
In case of the amorphous silicon thin film transistor (a-Si TFT), the active layer may be formed by depositing amorphous silicon in a short time, whereby a manufacturing time is relatively short and a manufacturing cost is reduced. Meanwhile, a carrier mobility in the active layer is low so that a current driving capacity is not good. Also, the amorphous silicon thin film transistor cannot be used for an active matrix organic light emitting device (AMOLED) due to a change of a threshold voltage.
In case of the polycrystalline silicon thin film transistor (poly-Si TFT), amorphous silicon is deposited and then crystallized. A process of manufacturing the polycrystalline silicon thin film transistor needs crystallization of the amorphous silicon so that a manufacturing cost is increased. Also, as the crystallization is carried out at a high temperature, it is difficult to apply the polycrystalline silicon thin film transistor to a large-sized device. In addition, it is difficult to ensure uniformity of polycrystalline properties in the polycrystalline silicon thin film transistor.
Meanwhile, in case of the oxide semiconductor thin film transistor, an oxide layer for the active layer is formed at a low temperature, a carrier in the active layer has high mobility, and a resistance of oxide is largely changed in accordance with an oxygen content, to thereby realize the desired properties with easiness. Also, the oxide semiconductor is transparent due to the properties of oxide so that it is possible to obtain a transparent display device with easiness. In this reason, an application of the oxide semiconductor thin film transistor has attracted great attentions. This oxide semiconductor may be formed of zinc oxide (ZnO), indium zinc oxide (InZnO), or indium gallium zinc oxide (InGaZnO4).